Scott raises some valid points. I would be hesitant to take a job of this magnitude if I didn't have control over the construction of the room and the wiring layout. It's too large an investment to leave the construction to a builder who knows how to make walls but almost certainly knows nothing about acoustics and proper soundproofing. Under NO circumstances would I allow an electrician to run the low voltage wiring. Inferior wire will be used and electricians know nothing about proper speaker placement, what wires to run for a projector, etc.